When to use Volatile modifier?
java, volatile
Solution
volatile modifier will tell the JVM to be cautious of the threads which runs concurrently. Essentially, volatile is used to indicate that a variable's value will be modified by different threads.
Declaring a volatile Java variable means:
The value of this variable will never be cached thread-locally: all reads and writes will go straight to "main memory"
Access to the variable acts as though it is enclosed in a synchronized block, synchronized on itself.
We say "acts as though" in the second point, because to the programmer at least (and probably in most JVM implementations) there is no actual lock object involved.
The volatile modifier tells the compiler that the variable modified by volatile can be changed unexpectedly by other parts of your program. One of these situations involves multithreaded programs.
In a multithreaded program, sometimes, two or more threads share the same instance variable. For efficiency considerations, each thread can keep its own, private copy of such a shared variable.
The real (or master) copy of the variable is updated at various times, such as when a synchronized method is entered. While this approach works fine, it may be inefficient at times. In some cases, all that really matters is that the master copy of a variable always reflects its current state.
To ensure this, simply specify the variable as volatile, which tells the compiler that it must always use the master copy of a volatile variable (or, at least, always keep any private copies up to date with the master copy, and vice versa). Also, accesses to the master variable must be executed in the precise order in which they are executed on any private copy.
Problem
Possible Duplicate: When exactly do you use the volatile keyword in Java? When and why volatile modifier is required in java? I am interested in seeing a real world usage of a volatile modified primitive or object reference.